Alloys for high temperature service use



Patented Feb. 27, 1945 ALLOYS FOR HIGH TEMPERATURE SERVICE USE Hugh S.Cooper, Cleveland, Ohio No Drawing. Application March 1'7, 1942,

Serial No. 435,009

2 Claims.

This invention relates to metallurgy and more particularly to asubstantially non-ferrous alloy composition suitable for use in themanufacture of valves for automotive and aviation engines, oil crackingtubes, steam boiler tubes, turbine.

blades, and the like articles, where high temperature oxidation,corrosion and erosion resistance combined with high hardness and withhigh tensile strength and a low creepv value at high temperatures areessential properties desired in ad-.

dition to suflicient ductility at a hot working temperature to permitthe mechanical deformation of the alloy to the desired size, shape andconfiguration.

One of the objects of the present invention is to provide an alloypossessing all of the properties defined above.

Another object is to provide an alloy suitable for use in the articlesdefined above.

Still another object is to provide a high temperature oxidation,corrosion and erosion resistant alloy possessing a relatively hightensile strength and low creep value at elevated temperatures and a highhardness value at said elevated temperatures.

Other objects and advantages will be apparent as the invention is morefully hereinafter disclosed.

In accordance with these objects I have disremaining alloy compositionappears to result.

In general, I prefer maintaining the Cr content within the range to andthe iron content at approximately the minimum within the range of 10 tothat will dissolve the Ta or Cb and the carbon, while the Mn content ismaintained as low as is possible'to obtain a substantially deoxidizedalloy.

It may be seen, therefore, that with any given Ta or Cb and carboncontent within the ranges specified, the minimum solutioning Fe contenttherefor, the physical properties of the alloy may be widely varied byvarying the relative proportioning of the metals Ni and Co comprisingthe base while maintaining the Cr content substantially constant withinthe range 15 to 20%.

As one specific example, the combination of I elements giving themaximum hot forgeability with high tensile strength will be described.This alloy contains at least one of the metals Cb and Ta about 3.0%,carbon about .50%, Fe about 15%, Mnabout 1.5% and Cr about 15%, theremainder consisting of Co and Ni in the ratio of about two (2) parts Nito one (1) part Co and in total amount constituting about 65% of thealloy. This alloy shows a tensile strength at about 1500 F. of about69,000 pounds persquare inch and at 1800| F. shows a tensile strength ofabout 33,000

pounds per square inch. The hardness of the alloy at atmospherictemperatures approximates 275-300 Brinell.

The tensile strength of this alloy is materially increased by loweringthe nickel content of the base which results in a material loss inductility at temperatures within the range 1800-2200 F.

interfering with mechanical deformation, and

tensile strength at temperatures within the range 1500-4800 F.,excellent oxidation, corrosion and erosion resistance at alltemperatures up to 1800" F. and a relatively high hardness whichpersists to elevated temperatures approximating 1800 F. and requiringthe use of forging temperof the remainder. the maximum workabilityforany given remaining alloy composition appears to result. When thenickel content of the remainder is lowered to small fractionalpercentages, the maximum tensile strength for any given also in a lossin machinability. The ductility of the alloy at forging temperature andthe machinability may also be markedly improved by raising the ironcontent of the alloy somewhat. For example, with Ni under 10% the Feshould be raised to 25% to obtain equivalent ductility at the forgingtemperature and equivalent machinability in the higher tensile strengthalloy. In this respect, Fe and Ni are equivalents. However, with respectto the solutioning of the Ta and Cb carbides present, Fe and Ni are notsubstantial equivalents, and it appears necessary to maintain at least a15% Fe content in the alloy for this purpose.

Where greater hardness is desired to improve either the erosionresisting properties or the creep strength of the alloy at elevatedtemperatures. the Ta and Cb carbide content of the alloy may beincreased within the ranges given, said inthe Co is in excess to the Ni.

crease being made at the expense of the remainder base (Co and Ni). Formost purposes, however, from 2 to 3% of at least one of the elements Taand Cb appear adequate to impart a satisfactory creep strength andhardness giving a reasonably consistent long life under the usualservice conditions experienced in the several fields of use contemplatedfor the alloy.

The. corrosion and high temperature oxidation resistance of the alloyappears adequately taken care of by the chromium content of toparticularly in those alloy compositions wherein As the Ni contentapproaches the same percentage as the Co, the Cr content preferablyshould .be maintained as close to 20% as practicable.

Valves for internal combustion engines, particularly aviation engines,are subjected to severe erosion and corrosion at relatively hightemperatures besides repeated deformation stresses incident to theseating of the valve on the seat.

Valves comprised of the alloy of the present invention have been foundto be greatly superior to other alloys heretofore employed and to give amuch longer service life.

Oil cracking tubes made from the alloy of the present invention may beused safely at temperatures and pressures not heretofore possible withother alloys. Steam boiler tubes, particularly steam superheater tubes,made from the alloy of the present invention also may be used attemperatures and pressures not heretofore possible with other alloys.

Turbine blades made from the alloy composition of the present invention,such as in turbines operating the superchargers of aviation engines arestronger and more durable than blades comprised of any other alloyheretofore proposed.

Having hereinabove described the present invention generically andspecifically and given one specific embodiment thereof with severalcontemplated modifications thereof, it is believed that it is apparentthat the same may be widely varied without essential departure therefromand all such are contemplated as may fall within the scope of thefollowing claims.

What I claim is:

1. An alloy composition characterized by high temperature oxidationresistance, corrosion and erosion resistance with high hardness and withhigh tensile strength as well as low creep value at high temperatures,said alloy consisting of Cr 15 to 20%, Fe 10-25%, at least one of themetals Ta and Cb l5%, Mn .50-2.0%, carbon .35.75% with the balance ofthe alloy consisting of Ni and Co, the Ni content of said balance beingwithin the range from small fractional percentages up to 60% of saidbalance and the said iron content within the range 10 to 25% being atleast sufficient to effect substantially complete solution of thecarbide compounds of Ta and Cb present in the said alloy.

2. A high tensile strength hot forging alloy, said alloy having a Crcontent approximating 15%, an Fe content approximating 15%, an amount ofone of the metals Cb and Ta approximating 3%, carbon approximating Mnapproximating 1.5% with the balance of the alloy consisting of Ni and Coin the ratio of two parts Ni to one part Co, said alloy beingcharacterized by a hardness at atmospheric temperatures approximating275-300 Brinell.

HUGH S. COOPER.

